1. Field of the Invention
This invention relates generally to tire pressure monitoring systems, and more particularly is directed towards a new and improved method and apparatus for monitoring tire pressure in which a sound signal from a tire pressure signal-generating device is uniquely coded and processed to distinguish it from background noise for the purpose of preventing false alarm signals. This invention also relates to a tire pressure monitoring system adapted to calculate the rate of loss of tire pressure in a leaking tire and indicate the time remaining until the vehicle becomes immobile.
2. Description of the Prior Art
It is known that the pressure of a pneumatic tire may be monitored for either low or high pressure by means of a device mounted to the wheel and adapted to generate a sound signal upon the occurrence of a high or low pressure event. The sound signal is then detected by a transducer forming part of a processing system for actuating an alarm device to alert the driver of a vehicle. By way of example, U.S. Pat. Nos. 3,489,998; 3,738,308; 3,890,595 and 3,934,223 show systems of this type. In these systems, measures have been considered to prevent false signals resulting from background noise rather than actual sound signals from the wheel device by means of filtering techniques. In such systems the sound signal generating devices are set to emit a predetermined frequency which is detected and filtered by appropriate electronic circuitry. However, such systems, while effective over a wide range of ambient noise conditions, nevertheless may be subject to responding to false signals which may occur from background noise within the predetermined frequency range. By way of example, tire squeal, transmission sounds, brake squeal and the like, which fall within the selected frequency range may trip the system and produce a false alarm signal.
It is an object of the present invention to provide improvements in systems of the foregoing type, and more particularly to provide a novel method and associated apparatus for coding and detecting signals from a sound signal generator in such a manner to actuate the signal sensing and processing system to the exclusion of all other ambient undesired acoustical signals.
Another object of this invention is to provide a tire pressure monitoring system adapted to detect rate of pressure loss and indicate the remaining time and/or pressure before the tire renders the vehicle immobile.